The invention relates to a method of manufacturing a plastics pipe, with a circular cross section, comprising an outer pipe and an inner pipe, which is concentrically arranged with respect to the outer pipe, and petitions extending in the longitudinal direction of the pipe and connecting the outer pipe with the inner pipe, by pressing a mass of synthetic material through a space, delimited by an outer and an inner annular support, in which pin-shaped supports are disposed in spaced relationship from each other, which are adapted to the cross section of elongated channels to be formed in the wall of the plastics pipe.
Such a method of manufacturing plastics pipes with a circular cross section, comprising an outer pipe and an inner pipe which is concentrical thereto and partitions extending in the longitudinal direction of the pipe is known.
This method in which an extruder with an annular mouthpiece, with pins for the formation of the channels, is used, has the drawback that in manufacturing a plastics pipe in which between the inner and outer wall of the pipe are a row of channels with a circular cross section, longitudinal ridges are formed, also called: corrugations. These longitudinal ridges or corrugations make the pipes unfit for various purposes, while moreover the strength properties of such pipes leave much to be desired.
On the other hand, however, plastics pipes with only one row of elongated channels between the inner- and outer wall are in great demand. Contrary to pipes with more concentric rows of annular channels between the inner- and outer wall less material is required for obtaining the same rigidity, whereas another advantage is a decreased buckling length and a simpler output.